A two-stage switch valve is known (e.g., JP 2005-291241 A corresponding to US 2005/0217734 A1), in which a valve element slides in a flow passage to switch a cross-sectional area of the flow passage. The two-stage switch valve includes the valve element having an outer peripheral edge slidably supported in the flow passage, and a spring urging the valve element upstream in the flow passage.
When a fluid pressure on an upstream side of the valve element in the flow passage increases, and when a pressure on the valve element increases, the valve element moves downstream against an urging force of the spring, and thereby reduces the cross-sectional area of the flow passage. More specifically, when the valve element moves to a downstream valve position, a fluid is prevented from flowing on an outer side of the valve element to bypass the valve element. Thus, the fluid flows only through a communication hole provided in the valve element.
On the other hand, when the fluid pressure on the upstream side of the valve element in the flow passage decreases, and when the pressure on the valve element decreases, the valve element moves upstream by the urging force of the spring, and thereby increases the cross-sectional area of the fluid passage. More specifically, when the valve element moves to an upstream position, the fluid flows on the outer side of the valve element to bypass the valve element with flowing through the communication hole of the valve element. Therefore, the sliding of the valve element causes switching of the cross-sectional area of the flow passage. Accordingly, the fluid pressure is regulated and a flow rate of the fluid is adjusted.
The valve element has a circular plate shape and has a circular cylindrical slide surface that is slidably supported by a cylindrical guide wall surface of the flow passage. In this case, the valve element is high in aspect ratio that is a ratio between a diameter of the valve element and a dimension of the valve element in its sliding direction. Thus, if the valve element inclines slightly, the valve element may get stuck in the flow passage and be difficult to slide on the guide wall surface. Thus, the structure of the valve element may cause malfunction of the two-stage switch valve.